Dehumidifying composition and a method for preparing the same

ABSTRACT

A dehumidifying composition intended for the dehydration of hermetically sealed containers of various shape and capacity, small-capacity containers inclusive, which contains 20-60 wt. percent of zeolite and 40-80 wt percent of thermosetting polymer. Said polymer may be obtained by curing diverse thermosetting resins such as, for example, epoxide and phenol-formaldehyde resins. The dehumidifier of the invention finds application in the form of a film or coat strongly bonded to the material of the containers being dehydrated and no special means are required for securing it in the containers used in conjunction with diverse semiconductor devices and instruments.

United States Patent Plachenov et al.

[451 Dec.5, 1972 [54] DEHUMIDIFYING COMPOSITION AND A METHOD FORPREPARING THE SAME [72] Inventors: Tilthon Grigorievich Plachenov,Leningrad; Grigory Markovich Belotserkovsky, Leningrad; EkaterinaNikolaevna Dolgova, Leningrad; Jury Valentinovich Ezhov, Leningrad;Vladimir Alexandrovich Fogel, Leningrad; Andrei Pavlovich Benedlktov,Zelenogorsk; lliya Yakovlevich Avilov, Leningrad, all of U.S.S.R.

[73] Assignee: Lenlngradslty Tekhnologichesky lmeni Lensoveta,Leningrad, U.S.S.R.

[22] Filed: Jan. 6, 1971 [21] App|.No.: 104,480

[52] 0.8. CI ..220/64, 117/95, 117/161 ZB,

252/194, 260/37 EP, 260/38 [51] Int. Cl. ..B65d 25/14 [58] Field ofSearch ..260/37 EP, 38; 252/194;

Primary Examiner-Edward G. Whitby Attorney-Waters, Roditi, Schwartz &Nissen [5 7] ABSTRACT A dehumidifying composition intended for thedehydration of hermetically sealed containers of various shape andcapacity, small-capacity containers inelusive, which contains 20-60 wt.percent of zeolite and 40-80 wt percent of thermosetting polymer. Saidpolymer may be obtained by curing diverse thermosetting resins such as,for example, epoxide and phenol-formaldehyde resins. The dehumidifier ofthe invention finds application in the form of a film or coat stronglybonded to the material of the containers being dehydrated and no specialmeans are required for securing it in the containers used in conjunctionwith diverse semiconductor devices and instruments.

. 8 912 2 fiq raiz w DEHUMIDIFYING COMPOSITION AND A METHOD FORPREPARING THE SAME This invention relates to dehumidifiers intended fordehydration of hermetically sealed containers of varied shape andcapacity, small-capacity containers inclusive, and to a method forpreparing the same. The present invention is primarily concerned withmaintaining constant humidity in casings and enclosures forsemiconductor devices and integrated circuits in order to provide forparameter stability and performance reliability of said devices andcircuits.

The dehumidifying composition, according to the present invention, maxlikewise find application for desiccating the interior of diverseoptical instruments "such as, for example, optical tubes.

Silica gel, barium oxide calcium oxide, and zeolites are knowndehumidifiers for semiconductor devices, various techniques of disposingand securing said dehumidifying agents in the casings of semiconductordevices being known in the art. Silica gel, barium oxide, calcium oxide,and zeolites are used in conjunction with electronic devices in the formof powders, granules or compressed tablets, the employment of silica geland zeolites as silicone oil-based fluid or thickened mixtures beingalso feasible. At present three methods of securing variousdehumidifiers in the casings of electronic devices are practiced on anindustrial scale. 1. A granular, powdered or tabletted dehumidifier isplaced in a special recess provided in the device casing and separatedfrom the casing interior with a fine gauze fabricated from a porousmetal such as, for example, nickel. However, this method of dehumidifieremployment makes the design of devices excessively elaborate, does noteliminate the possibility of finely pulverulent dehumidifier depositionon the surface of PN junctions, calls for additional steps in theprocess of electronic device manufacture and also for the use ofspecial-type processing equipment and accessories, effects adversely theproductive capacity and increases the cost price. This method is furtherdisadvantageous in that it is inapplicable for introducing and securinga dehumidifying agent in the casings of miniaturized devices.

2. Dehumidifier granules or tablets are secured in the casings ofdevices with resin-based adhesives. This method is incapable ofproviding an adequate mechanical strength of dehumidifier bond to thecasing, while the thus bonded granules or tablets tend to deteriorate inthe course of device operation and evolve fine particles which arelikely to short-circuit the PN junctions, thereby necessitating theprotection of device surfaces with varnish coating which generallyimpair the performance parameters. The method is highly laborious andprovides no reliable means of checking the strength ofdehumidifier-to-casing bonding. A further disadvantage of this method isassociated with the fact that a wide range of dehumidifier tablet sizesis required for use in conjunction with various types of devices.

3. The third known method consists in employing fluid or thickenedmixtures of silicone oils with aerosil or zeolite powders and suffers,like the two previously described methods, from major limitations, suchas the employment of special-type processing equipment, a cumbersomeprocedure required for dehumidifying mixture preparation, and the dangerof silicone oil penetration onto the container flanges, the latterlimitation being responsible for a high percentage of rejects and forthe necessity of monitoring 100 percent of the finished devices forhermetic seal. Moreover, silicone oils of the purity required by themethod under consideration are critical, while the employment ofsilicone oils having inadequate purity results in impairing theperformance reliability and parameter stability of the devices. Thismethod is further disadvantageous in that the prepared thickened mixturedoes not lend itself to regeneration and has a limited shelf life (up to72 hours) prior to mixture introduction into containers, so that it isimpracticable to provide a thickened mixture stock.

It is an object of the present invention to provide a dehumidifier forthe dehydration of hermetic containers of various capacity and shapeused in diverse devices and instruments which will make it possible toattain high performance reliability and parameter stability of devicesand instruments, will lend itself to repeated regeneration, will have anunlimited shelf life, will offer greater application convenience ascompared to the known dehumidifying agents, and will be conducive tominimizing the percentage of rejects and the costs of production ofdevices and instruments that incorporate hermetic casings.

lt is another object of the present invention to provide a dehumidifierwhose rate of water vapor absorption can be varied depending uponspecific requirements, as well as upon the microclimate in industrialpremises and the duration of device assembling operations.

These and other objects are accomplished by the provision of adehumidifying composition for the dehydration of hermetic containers ofvarious shape and capacity, small-capacity containers inclusive. Thedehumidifying composition, according to the present invention, consistsof from 20 to 60 wt. percent of zeolite and from 40 to wt. percent of athermosetting polymer capable of forming a cohesive bond with zeoliteand an adhesive bond with the material of a hermetic container (casing)to be dehumidified.

Said thermosetting polymer may consist of cured epoxide resin or curedphenol-formaldehyde resin, or a mixture thereof. It is likewise feasibleto employ other resins such as, for example, urea-phenol-formaldehyde ormethylpolymide resins.

Use can be made of diverse modifications of said dehumidifyingcomposition for example, the preferred dehumidifying compositioncomprises 40 wt. percent of Type Na zeolite A and 60 wt. percent ofcured plasticized epoxide resin containing l8 wt. percent of epoxygroups, the advantages offered by said preferred composition being asfollows: a higher efficiency which manifests itself in superior adhesionof the composition in question to metallic surfaces and in enhancedmechanical strength of the resultant coating; the absence of crumblingor dusting phenomena in the applied composition, which property isessential in evaluating the quality of finished devices or instruments.

The present dehumidifying composition is preferably used in the form ofa film or coat applied to a part of the interior surface of hermeticcontainers (casings).

The dehumidifier film or coat is strongly bonded to the material of acontainer being dehydrated, so that no additional means or operationsare required for securing said dehumidifier composition in saidcontainer.

The method of obtaining the present dehumidifying composition in theform of a film or coat comprises applying onto the inner surface ofcontainers a suspension containing 100 parts by weight of zeolite havinga humidity of 20-23 wt. percent, 45-280 parts by weight of athermosetting resin, 120 parts by weight of an organic solvent intendedfor dissolving said resin, -45 parts by weight of a suitableplasticizer, and 0-85 parts by weight of a curing agent.

The suspension applied onto the inner surface of a container ismaintained in the air at a temperature of from 5 to 80 C in order toremove the bulk of volatile components, followed by subjecting saidsuspension to heat treatment in vacuo at a residual pressure of notgreater than mm Hg and at a temperature of from 150 to 180 C. Said heattreatment removes the last traces of volatile components, brings aboutbinder polymerization and results in the formation of film or coat(layer) depending upon the amount of the suspension used, said film(coat) being characterized by a highly extended porous structure whichis adhesively bonded to the coated surface and provides for therequisite kinetics of water vapor adsorption. The porous structure of adehumidifying composition film is defined by the volume of primary poresin zeolite crystals and by the volume of secondary pores. The volume ofsecondary pores depends primarily on the dispersity of zeolite crystalsand binder (resin) particles, as well as on the nature of the binderused, and the type and density of zeolite crystal and binder particlepacking.

The volume of secondary pores in the range of equivalent radii of from291,000 to 31 A equals 0.044 em /em a significant portion of said volume(0.020 cm lcm being due to the pores in the equivalent radius range offrom 98 to 3l A wmnwmm M An essential feature of the presentdehumidifying composition is that it provides the possibility ofcontrolling the kinetics of adsorption by varying the proportion ofcomponents of stock suspensions, so that the present dehumidifyingcomposition can be used in devices and instruments of various types andsizes, the desired kinetics of moisture adsorption inside a given device(instrument being attained by selecting an appropriate ratio ofsuspension components. As compared to the known dehumidifying agents inthe form of tablets or thickened silicone oil-based mixtures, thepresent dehumidifying composition in the form of a film or coat occupiesa very small volume inside casings and has an insignificant weight. Saidbeneficial characteristics of the present dehumidifying composition makeit eminently suited for use in conjunction with microminiaturizedelectronic instruments. The dehumidifying composition contained in aninstrument casing (bulb) can be repeatedly regenerated, thereby makingit practicable to have a requisite stock of dehumiditier-coated casings,a further advantage of the present dehumidifier being the absence of oilon the surfaces to be welded and, hence, the ease of sealinghermetically the devices or instruments.

The present dehumidifying composition is employed without resorting tomechanical means for securing said composition in instrument (device)casings or to special-type equipment for introducing said compositioninto instrument (device) casings and is suitable for being introducedinto casings (bulbs) of any shape or size at one and the same productionsection, the latter feature being highly advantageous for thesimultaneous production of diverse types of semiconductor instruments.It is expedient to use the present dehumidifying compositionirrespective of the scale or automation degree of production processesor when the manufacture of instrument casings and the assembly offinished semiconductor devices are carried out at different plants.

It follows from the foregoing that the present dehumidifying compositionused in the form of a film or coat is commercially superior to the knowndehumidifiers.

The following examples are illustrative of the manner of carrying outthe invention but are not intended to limit the scope thereof.

EXAMPLE 1.

One hundred parts by weight of Type Na zeolite A (moisture content, 25percent by weight; particle diameter, 4 me maximum) is mixed with partsby weight of epoxide resin (molecular weight, 370-450; epoxy groupcontent, 18 percent) dissolved in 127 parts by weight of an organicsolvent having the following composition, percent by weight: butylacetate, 10; cellosolve (C H OCH CH OH), 8; acetone, 7; butanol, 15;ethanol, 10, and toluene, 50. Dubutyl phthalate (plasticizer) is addedto the stirred mixture in an amount of 5 parts by weight, followed byintroducing 10 parts by weight of polyethylene polyamine (curing agent).The resulting mixture is thoroughly mixed to obtain a homogeneoussuspension. The dehumidifying composition thus prepared is ready foruse.

Use is made of a buret, an atomizer or a syringe to apply thecomposition on the inner surface of instrument metal casings (bulbs)having a volume of 0.25 cm. From 10 to 12 mg of said composition isintroduced in each bulb, followed by maintaining the bulbs with saidcomposition applied thereonto for a period of 10-20 hours in the air atambient temperature in order to remove the bulk of volatile components.Next the bulbs are placed in a vacuum drying cabinet, subjected togradual heating to a temperature of C at a residual pressure of 0.1 mmHg, and maintained at this temperature for a period of 3 hours. It ispertinent to gradually heat the composition in order to provide in theresultant film an access of zeolite micropores to the ambient atmosphereand to attain good adhesion of the film to the bulb surface. Theresultant film displays heat stability up to a temperature of 200C inthe air. The thus-treated bulbs are ready for use as sealing componentsof instruments or circuits.

Mechanical tests of the film under the conditions prescribed for testingtransistors enclosed in bulbs are indicative of the absence ofcrumbling, dusting or cracking phenomena.

The film obtained by the procedure described herein before is capable ofmaintaining in the hermetically sealed volume of the bulb a low relativehumidity in the temperature range of from -60 to +1 50C.

The kinetics of water vapor adsorption inherent in said film makes itpossible to keep the bulbs with the film applied on the inner surfacethereof for a period of 1 hour under humid microclimatic conditions (dewpoint, 30C). Thanks to a relatively low rate of water vapor adsorptionby the film, the bulbs may be brought in contact with the ambientatmosphere for a period of 12 minutes.

In case the period of time between film application and the use ofthus-treated bulbs for instrument sealing exceeded one hour, said bulbs,prior to use, should be maintained at a temperature of 160180C and undera vacuum of at least 0.1 mm Hg for 3 hours. This procedure results infilm regeneration and the total restoration of moisture absorbingproperties of the film irrespective of the time of film contact withatmosphere.

If the bulbs with a film applied thereonto are stored in sealedampoules, film regeneration can be dispensed with and the shelf life ofsaid bulbs under these conditions is quite long.

The results of testing various devices enclosed in bulbs coated on theinside with films of the present dehumidifying composition are asfollows.

The transistors display steady parameters such as, for example, steadyback currents and amplification factors, the parameters remainingconstant after any period of maintaining the instruments in question ata temperature of 1 120C. The instruments withstood the most rigorousmechanical tests, prolonged vibration and repeated impact testsinclusive.

Said bulbs were likewise employed for sealing superhigh frequency planarsilicon transistors, and the presence of the dehumidifying compositionprovided for enhanced parameter stability during instrument serviceunder the conditions of sharp temperature variations in the range offrom -60 to +l 80C, the amplification factor and back currents beingexemplary steady parameters.

Where the proportions of the present dehumidifying compositioncomponents are varied so that the composition contains a lowerproportion of epoxide resin and a higher proportion of zeolite, theresultant film exhibits, in contrast to the film described hereinbefore, an essentially higher rate of water vapor adsorption.

EXAMPLE 2.

One hundred parts by weight of Type Na zeolite A (moisture content, 25wt. percent; particle size, 4 mo maximum) is mixed with 150 parts byweight of resoltype phenol-formaldehyde resin (in combination withpolyvinyl butyral) dissolved in 125 parts by weight of the solventdisclosed in Example 1. The components are mixed until a homogeneoussuspension is obtained. The resultant suspension is ready for use.

The dehumidifying composition film is prepared by following theprocedure of Example 1.

Relevant tests have shown that the film is capable of providing a lowrelative humidity in a closed volume of a bulb. The instruments sealedwith bulbs furnished with the film prepared as described above displayparameter stability and enhanced performance reliability at temperatureof up to 120C. However, the film exhibits a somewhat inferior elasticityand suffers from slight crumbling and dusting when transistor devicesare subjected to mechanical tests such as, for example, vibration testsand repeated impact tests.

Hence, the dehumidifying composition based on phenol-formaldehyde resinin combination with polyvinyl butyral is noted for its goodmoistureabsorbing pro perties and may be used to advantage in instruments anddevices operated in the absence of significant mechanical loads.

EXAMPLE 3 One hundred parts by weight of Type Na zeolite A (moisturecontent, 25 wt. percent; particle diameter, 4 mc maximum) is mixed witha binder consisting of 250 parts by weight of 60 percent resol-typephenol-formaldehyde resin, 50 parts by weight of a solution of epoxideresin in methyl ethyl ketone, and 10 parts by weight ofhexamethylenetetramine. The mixture components are thoroughly mixed inthe organic solvent disclosed in Example 1 until a homogeneoussuspension is obtained.

The film prepared from said dehumidifying composi tion and theinstruments sealed with a bulb coated with said film have the propertiesidentical to those of the film and instruments disclosed in Example 1,respectively.

We claim:

1. A dehumidifying composition for dehydration of hermetically sealedcontainers which consist of a zeolite and a thermosetting polymercapable of forming a cohesive bond with the zeolite and an adhesive bondwith the material of said containers, the content of zeolite in saidcomposition being from 20 to 60 wt. percent and the content of saidpolymer being from 40 to wt. percent, and said composition has asignificant portion of the volume of its secondary pores due to pores inthe equivalent radius range of from 98 to 31 A.

2. A dehumidifying composition according to claim 1, wherein thethermosetting polymer is cured epoxide resin.

3. A dehumifidying composition according to claim 1, wherein thethermosetting polymer is cured phenolformaldehyde resin.

4. A dehumidifying composition according to claim 1, wherein thethermosetting polymer is a cured mixture of epoxide resin andphenol-formaldehyde resin.

5. A dehumidifying composition according to claim 1, which comprises 40wt. percent of Type Na zeolite A and 60 wt. percent of cured andplasticized epoxide resin containing 18 percent of epoxy groups.

6. A method of preparing a dehumidifying composition in the form of afilm or coat intended for dehydration of hermetically sealed containersof various shape and capacity, small-capacity containers inclusive,which comprises applying onto a part of the inner surface of saidcontainers a suspension containing 100 parts by weight of zeolite,45-280 parts by weight of thermosetting resin, parts by weight of asolvent capable of dissolving said resin, 045 parts by weight of asuitable plasticizer, and 0-85 parts by weight of a suitable curingagent; maintaining the applied suspension at a temperature of from 15 to80C in order to remove the bulk of volatile components, and thereaftersubjecting said suspension to heat treatment at a temperature of from toC in vacuo under a residual pressure of 10 mm Hg maximum, said heattreatment resulting in the removal of the last traces of said solventand in the formation of a microporous film which adhesively coats saidsurface of said containers 7 8 p and exhibits the requisite kinetics ofwater vapor ad- 8. A hemetically scalable container for providingsorption. a moisture free environment for enclosing moisture enclosllfl?f pfovldlqg q sensitive equipment having at least some portion ofvlfonmem wmPrl-Smg a comamer for said environits inner surface coatedwith a film of the dehumidifyment, having at least some portion of itsinner surface 5 ing composition of claim coated with a film of thedesiccant composition of claim 1.

2. A dehumidifying composition according to claim 1, wherein thethermosetting polymer is cured epoxide resin.
 3. A dehumifidyingcomposition according to claim 1, wherein the thermosetting polymer iscured phenol-formaldehyde resin.
 4. A dehumidifying compositionaccording to claim 1, wherein the thermosetting polymer is a curedmixture of epoxide resin and phenol-formaldehyde resin.
 5. Adehumidifying composition according to claim 1, which comprises 40 wt.percent of Type Na zeolite A and 60 wt. percent of cured and plasticizedepoxide resin containing 18 percent of epoxy groups.
 6. A method ofpreparing a dehumidifying composition in the form of a film or coatintended for dehydration of hermetically sealed containers of variousshape and capacity, small-capacity containers inclusive, which comprisesapplying onto a part of the inner surface of said containers asuspension containing 100 parts by weight of zeolite, 45- 280 parts byweight of thermosetting resin, 120 parts by weight of a solvent capableof dissolving said resin, 0-45 parts by weight of a suitableplasticizer, and 0-85 parts by weight of a suitable curing agent;maintaining the applied suspension at a temperature of from 15* to 80*Cin order to remove the bulk of volatile components, and thereaftersubjecting said suspension to heat treatment at a temperature of from150* to 180*C in vacuo under a residual pressure of 10 1 mm Hg maximum,said heat treatment resulting in the removal of the last traces of saidsolvent and in the formation of a microporous film which adhesivelycoats said surface of said containers and exhibits the requisitekinetics of water vapor adsorption.
 7. An enclosure for providing amoisture-free environment comprising a container for said environment,having at least some portion of its inner surface coated with a film ofthe desiccant composition of claim 1.